The present invention is related to Japanese patent application No. Hei. 11-291,244, filed Oct. 13, 1999; the contents of which are incorporated herein by reference.
This invention relates to a route-setting device for setting a route to a destination, and more particularly to a route setting device that guides traveling along the set route.
Conventional navigation systems can detect a present position by using GPS in the traveling vehicle. This system can display the present position on a display screen together with a road map, and guide the traveler along a suitable route set from the present position to the destination. This enables the user to smoothly drive to a desired destination. The route is set, generally, based upon the Dijakstra method or a similar method. Specifically, the route calculation cost (evaluation value of the route) is calculated from the present position to nodes by using map data stored in a static data source such as a CD-ROM or a DVD and by using link data for the links among the nodes. Links, having a minimum cost, are connected together to set a route to the destination after all costs up to the destination have been calculated.
Plural modes of operation can be used to set a route. These plural modes include a time-priority mode for setting a route that minimizes the traveling time, a distance-priority mode for setting a route that minimizes the traveling distance, and a common road-priority mode for setting a route that avoids toll roads as much as possible.
For the time-priority mode, the evaluation value of the road is the time needed for passing through the road as calculated based on expected average vehicle speeds, and a combination of roads is selected such that the sum of evaluation values for traveling from the start point to the destination becomes a minimum, thereby setting a route which minimizes the traveling time.
In the distance-priority mode, the evaluation value of the road is the length of the road, and a combination of roads are selected such that the sum of the evaluation values becomes a minimum, similar to the time-priority mode, thereby setting a route which minimizes the traveling distance.
In the common road-priority mode, the evaluation value for the toll road is adjusted larger (by, for example, 10 times) than the ordinary case based on, for example, the evaluation value of the time-priority mode. This relatively increases the sum of the evaluation values of when the user travels toll roads. Thus, the set route avoids toll roads as much as possible. The evaluation values that serve as a reference may be for the distance-priority mode or other criteria. Thus, the desired route is selected out of these modes. Namely, the route can be set to meet the user""s demand, such as placing priority on the time, distance or common roads.
However, when the start point, passing point or destination is set on a toll road, requiring the user to use the toll road, then a very long roundabout route may be set depending upon road conditions if set in the common road-priority mode. This occurs because the evaluation value for the toll road is multiplied by ten folds. Accordingly, even a slight difference in the traveling distance of the toll road results in a great difference in the evaluation value. For example, avoiding a toll road as short as 300 meters may result in setting a route which goes through a common road as long as 3000 meters. Moreover, the user may find it strange when a route is set in a different direction from that contemplated by the user, in addition to traveling a long distance. For example, if a service area is set as the start point, the distance to an interchange located in the same direction as the destination is 10 Km and the distance to an interchange located opposite to the destination is 5 Km. Then, the difference is 5 Km, and a route is set over the common roads at a distance of 10 times 5 Km, i.e., to travel over a distance of 50 Km or less. This is undesirable since it goes toward the interchange opposite the destination, in addition to traveling about 50 Km of distance.
It is therefore an object of the present invention to set a desirable route and avoid particular roads where a start point, passing point or destination has been set on a particular road type.
In view of these and other objects, a route-setting device is provided for setting a route to a destination by calculating route evaluation values to the nodes based on the Dijakstra method, or other searching method that uses links connecting the nodes, and upon connection data among the links, and that connects links having a small total evaluation value from a start point to the destination. The device has a road-avoiding mode for setting a route to the destination, which avoids certain road types as much as possible. In one particular road-avoiding mode, the following route evaluation value is set. Here, the route evaluation value of the avoided road is set larger than the normal value. However, when the start point, the destination point or a passing point exists on the avoided road, the route evaluation value for that road (having a predetermined condition) is set to a relatively small value.
Here, the particular road is a particular road from the start point, destination or passing point on the particular road type to the nearest (next) outlet of the particular road. The particular road can be represented by a toll road or by an expressway in the toll road, a freeway, or a ferryboat route. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.